<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
    <style>
        
        .container {
            width: 500px;
            height: 300px;
            background: skyblue;
            display: flex;
        }
        .item:nth-child(1){
            width: 200px;
            height: 100px;
            background: pink;
        }
        .item:nth-child(2){
            width: 100px;  
            height: 100px;
            background: pink;
            flex-grow: 1;
            /* 其中一个写flex-grow:1; 它自己占满所有的剩余空间 200 */
            /* 它的宽度 100 + 200 */
        }
    </style>
</head>
<body>
    <div class="container">
        <div class="item"></div>
        <div class="item"></div>
    </div>
</body>
</html>